The present invention relates to apparatus for removing dust and/or other impurities from the surfaces of substantially flat objects. More particularly, the invention relates to improvements in apparatus for contact-free removal of dust or similar impurities from substantially planar surfaces of stationary or moving objects, especially flexible objects such as photographic films, photographic prints, webs of paper or textile material, strips or sheets of synthetic plastic or metallic material and the like. In addition to the just mentioned presently preferred uses of the improved apparatus, the latter can be used with equal advantage for removal of dust or other impurities from rigid or semirigid objects such as glass panes, mirrors, sheet- or plate-like filters and the like. Still more particularly, the invention relates to apparatus for removing solid impurities from the surfaces of substantially flat flexible or rigid objects, such as running webs of photosensitive material or stiff filters, by resorting to one or more streams of a gaseous fluid, particularly air.
In photographic copying and enlarging apparatus, particles of dust which adhere to the surfaces of originals are likely to affect the quality of images of originals on photographic paper or other suitable photosensitive material. Therefore, photographic copying and/or enlarging apparatus are normally provided with means for removing dust and/or other foreign matter from the surfaces of originals prior to exposure of originals to copying light. For example, German Offenlegungsschrift No. 1,497,401 discloses an apparatus wherein a source of compressed air discharges an air stream at an angle of less than 90 degrees against the surface of a web of flexible material (such as, for example, a strip of exposed and developed photographic film) which is transported through a copying machine. In accordance with the proposal in the just-mentioned German publication, the air stream impinges upon a concave surface of the running web. Therefore, the apparatus of the German publication cannot be used for adequate treatment of rigid or reasonably rigid bodies, such as mirrors, many types of filters for photographic light, opaque, transparent or translucent glass panes and the like. Moreover, it is often difficult (if not impossible) to adequately bend a flexible body (such as a strip or web of photographic material) in such a way that the surface which is to be cleaned by the air stream exhibits a desired or optimum degree of concavity. It was further found that conventional apparatus of the type disclosed in the German publication cannot satisfactorily remove all traces of dust or similar foreign matter. In order to provide an at least partly satisfactory cleaning action, apparatus of the just-described character must embody a source of compressed air which is capable of directing the air stream with a substantial force, i.e., the pressure of the air stream must be quite pronounced in order to ensure the removal of sufficient quantities of particulate matter from one or both surfaces of a web, strip or the like. The utilization of sources of highly compressed air contributes to the initial and maintenance cost of conventional apparatus and the operation of such apparatus invariably involves the generation of readily detectable noise which is bothersome and is likely to affect the productivity of the attendants.